[Pw_forum] Image charge interaction

[Thomas Brumme]

Dear Ilya,

Guiseppe is right and this is also the only way I think you can get
the image charge. You have to use the neutral Cl (i.e. no core
hole), put an extra electron, and force it to stay on Cl. This you
can try with +U (or SIC? or constrained DFT?). Anyway, in this
case you can end up with a dipole in the system and you need to
switch on the dipole correction. And you might get problems with
the homogeneous background if your vacuum is too large and
the area of your slab too small - the electrons could spill into the
minimum which is in the vacuum due to the background.

I don't know of any way of introducing a image charge in the
metallic slab by hand...

Thomas


On 09/13/2016 10:57 PM, Giuseppe Mattioli wrote:
> Dear Ilya
> I'm afraid there is not too much to add. You can test yourself the
> effect of sa emiempirical application of U by monitorizing the
> occupation of 3s and 3p Cl orbitals in some simple system like a Na
> and a Cl atom far from bond distance or a Cl[H2O]6(-) cluster to see
> when you get Cl(-). A polar solvent/medium stabilizes the excess
> charge and screen the interaction with images (see the role of
> dielectric constant in the old Makov-Payne paper) so that you should
> be able to use lower U values. I've still not published the psII
> calculations and I'm not sure that I will, because it turned out that
> structural results are in a closer agreement with experiment by using
> a GTO framework and COSMO as implicit dielectric environment.
> HTH
> Giuseppe
>
> Quoting Ilya Ryabinkin <igryabinkin at gmail.com>:
>
>> 2 Thomas:
>>
>>> Or you can also use the simple dipole correction which was actually
>>> developed for charged (particles on) surfaces, see, e.g.,
>> No, I think I wish the opposite: currently my pseudo-anion is neutral,
>> but the *real* one should not be -- and, hence, image charge
>> interaction is missing... I'd like to get it back.
>>
>> Of course, I it is possible and straightforward to keep an extra
>> electron on chlorine and simulate the system with real -1 charge, that
>> all what you've said are relevant and good.
>>
>> So, Giuseppe
>>
>>> I've used a semiempirical U value of 4 eV on the Cl 3p electrons to
>>> keep together the electrons of Cl- in photosystem II.
>> Could you elaborate more on that? Or may be you've published the
>> results -- I could read and reference them.
>>
>> Thanks to all of you, colleagues!
>>
>> --
>> I.

-- 
Dr. rer. nat. Thomas Brumme
Max Planck Institute for the Structure and Dynamics of Matter
Luruper Chaussee 149
22761 Hamburg

Tel:  +49 (0)40 8998 6557

email: Thomas.Brumme at mpsd.mpg.de